1. Field of the Invention
The present invention relates to a machine tool and, in particular, to a machine tool provided with a function to optimize a movement path in the machining of a workpiece.
2. Description of the Related Art
In conventional machining of a workpiece, a machining program is created and a machine tool is controlled based on this machining program to machine the workpiece. A machining speed for machining a workpiece is commanded as a movement speed of an axis in a machining program and indicates a maximum speed of the relative movement (tool movement) between a tool and a machining object based on the command. In the actual movement of a machine tool, the movement speed of the axis fluctuates at the start of machining or at a corner part, a curve part, or the like, according to an acceleration/deceleration time constant of each axis.
Further, as shown in FIGS. 8A and 8B, there is an allowable error relative to a target movement path of a tool in the machining of a workpiece. In order to maintain the accuracy of machining of a workpiece at a prescribed level, it is necessary to make an adjustment such that the tool moves within the range of the allowable error from a command path commanded by a machining program. Therefore, an operator of a machine tool conventionally makes, while confirming the machining surface accuracy of a machining object, an adjustment by changing an acceleration/deceleration time constant, changing a speed commanded in a program, etc.
As a related art associated with such machining of a workpiece, Japanese Patent Application Laid-open No. 2006-043836 discloses a method for setting machining conditions, in which machining path information is created and machining conditions are set using a machining pattern so as to reduce machining time while taking account of machining accuracy.
In a case where a machine tool is controlled so as to machine a workpiece, if a tool path deviates from a range that is defined by adding an allowable error to a command path commanded by a machining program, then a failure in a machining object or breakage of the machining object, tool, and machine tool may possibly occur. FIGS. 9A and 9B show examples in which a failure in a machining object (FIG. 9A) and breakage of a machining object or a tool (FIG. 9B) have occurred as a result of such deviation of a tool path during machining of a workpiece.
In general, a change amount from a position of an axis of a machine tool at certain time to a position of the axis at the next moment is indicated by data called a command pulse from a numerical control system. The command pulse is output to the machine tool as an outcome of interpolation processing, acceleration/deceleration control, or the like being carried out based on a command by a machining program. Such a command pulse output from the numerical control system is influenced by an acceleration/deceleration time constant of each axis set in the machine tool, and the acceleration/deceleration time constant of each axis is set by an engineer of a machine tool manufacturer when shipping the machine tool. In addition, the acceleration/deceleration time constant is also adjusted by an engineer of the machine tool manufacturer according to the characteristics of main machining objects, when installing the machine tool. Therefore, whether it is possible to acquire an optimum change amount depends on the experience and ability of an engineer of the machine tool manufacturer, the circumstances of the machining, or the like, and an optimum change amount cannot necessarily be acquired unconditionally.
In addition, the art disclosed in Japanese Patent Application Laid-open No. 2006-043836 is applicable only to a situation corresponding to a given machining pattern and does not enable flexible response to a wide diversity of situations.